1. Field of the Invention
The present invention relates to MEMS (Micro-Electronic Mechanical System) technology. More particularly, the present invention relates to a metal wiring method capable of connecting a metal wiring to a via hole having an undercut.
2. Description of the Related Art
A prospect of MEMS Market development shows rapid growth in that MEMS technology adopts semiconductor manufacturing techniques, thereby realizing bioengineering related technology and products such as protein chips, DNA chips and micro machining, which are nano-meter level microminiature three-dimensional precision machinery structures.
MEMS technology adopts semiconductor fine manufacturing techniques, which repeat steps such as vapor deposition and etching, thereby enabling mass production of microminiature products at low prices. MEMS technology also uses electrostatic force, which is an attraction between charges, and surface tension as a driving force to generate current, thereby greatly lowering power consumption. The importance of MEMS technology grows as nano-technology and System On Chip (SOC) technology are developed.
Since a MEMS element may be easily broken, MEMS elements are tightly packaged or, more preferably, hermetically sealed, in order to be protected from dangerous circumstances.
A MEMS element packaged in this way may be referred to as a MEMS.
FIG. 1 illustrates a cross sectional view of a MEMS element 13 welded to a silicon wafer or substrate 12 and a glass wafer 14 according to the prior art.
Referring to FIG. 1, the MEMS element 13 is layered on the silicon substrate 12, and the glass wafer 14 is welded onto the silicon substrate 12 having the MEMS element 13 layered thereon.
A gyro chip, for example, may be used for the MEMS element 13, and an SOI (Silicon On Insulator) wafer may be used for the silicon substrate 12.
The silicon substrate 12 and the glass wafer 14 are welded using an anodic bonding technique, enabling hermetically sealed packaging when adapted to the MEMS element 13.
To connect wiring to the SOI wafer or silicon substrate 12, a glass wafer 14 having a via hole therein is used. A problem arises, however, when a via hole is bored into the glass wafer 14. Namely, an undercut 15 is formed on the glass wafer 14 when the via hole is bored therethrough. Evidence that such an undercut is formed may be seen in FIG. 2, which shows a Scanning Electron Microscopy (SEM) photograph of portion A of FIG. 1. In FIG. 2, undercuts may be easily seen around the via hole.
Undercuts such as these may cause a disconnection of metal wiring of the MEMS element or an increase in resistance and a decrease in yield of the device.
A method has been suggested for overcoming the undercut problem that uses a technique for boring via holes partially into a glass wafer using an etching solution, so that the via holes are not bored completely through the glass wafer. However, although the technique does not generate an undercut, some portions of the glass wafer have holes bored therein while other portions do not, and a manufacturing process becomes very complicated. Further, malformed holes may be formed, resulting in decreased yield of devices.
A manufacturing process becomes very simple if via holes are bored completely through the glass wafers. However, in such a case, excessive vapor deposition of a thin metal film for wiring is necessary, and the wiring may still be disconnected, or a yield of devices may be decreased.
In an effort to solve these and other problems, it is a feature of an embodiment of the present invention to provide a wiring method that allows a metal wiring to be connected to a glass wafer having an undercut formed therein.
According to a feature of an embodiment of the present invention, there is provided a metal wiring method for an undercut in a MEMS packaging process, the method including, disposing a MEMS element on a silicon substrate, welding a glass wafer to an upper portion of the silicon substrate having the MEMS element disposed thereon, the glass wafer having a hole formed therein for connecting a metal wiring, depositing a thin metal film for the metal wiring in the hole, and ion-mealing the deposited thin metal film.
In the ion-mealing of the method described above, the deposited thin metal film may be resputtered by injecting accelerated gas particles to strike the deposited thin metal film. Further, if the glass wafer has an undercut formed around the hole formed therein, the undercut is filled with the resputtered thin metal film. Further still, if the glass wafer has an undercut formed around the hole formed therein, the ion-mealing may be performed until the undercut is removed. The accelerated gas particles are preferably argon gas particles.